Search PubMed⌕ Search

Biomedical subjects

L Maffei

Publications and source records attributed to L Maffei.

At least 19 recordsLinked to original sources
PubMed1992

Simultaneous occurrence of monoclonal gammopathy and acute secondary leukemia with overexpression of P-glycoprotein.

A 52-year-old woman, previously treated with chemo- and radiotherapy for Hodgkin's disease, developed an acute non-lymphoid leukemia and, contemporarily, an IgG-kappa paraproteinemia. Cytogenetic analysis showed a major clone, representing 90% of observed metaphases, with monosomy of chromosomes 5 and 14. In addition, leukemic cells exhibited a high expression of the P-glycoprotein, a transmembrane glycoprotein involved in the multidrug-resistance mechanism. Possible explanations for this cluster of findings are provided.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Protein-DNA interactions in the 5'-flanking region of the bovine pancreatic ribonuclease gene.

In the 5'-flanking region of the bovine pancreatic ribonuclease gene a sequence has been identified which specifically binds one or more factors present in nuclear protein extracts prepared from bovine pancreas. The binding site, as delineated by footprinting analysis, is located in a region extending from positions -113 to -146 relative to the transcription initiation site of the ribonuclease gene. This region contains consensus sequences for known control transcriptional elements. The observed pattern of protein-DNA interactions is likely to be pancreas-specific as it could not be detected with nuclear extracts prepared from HeLa or bovine aorta endothelium cells.

Animals↗
PubMed1992

Exogenous supply of nerve growth factor prevents the effects of strabismus in the rat.

It has recently been reported that exogenous supply of nerve growth factor prevents the effects of monocular deprivation both in rats and in cats. Here we have extended these experiments to the case of strabismus. Repeated intraventricular injections of nerve growth factor were performed in rats made surgically strabismic early in the critical period. At the end of the critical period the ocular dominance distribution of visual cortical neurons was assessed in strabismic untreated, strabismic nerve growth factor-treated and strabismic Cytochrome C-treated (control) rats by means of extracellular recordings. We found that in rats surgical strabismus causes a consistent loss of binocular neurons. By contrast the treatment with nerve growth factor maintains the normal ocular dominance distribution of neurons in the primary visual cortex. We conclude that nerve growth factor exogenously supplied prevents the effects induced by surgical strabismus in rats and suggest that nerve growth factor has a role in visual cortical plasticity.

Animals↗
PubMed1992

Parvalbumin immunoreactivity: a reliable marker for the effects of monocular deprivation in the rat visual cortex.

In mammals, monocular deprivation performed during the early stages of postnatal development (critical period) dramatically affects the functional organization of the visual cortex. Since the early work of Hubel and Wiesel, the effects of monocular deprivation are accounted for by the fibers driven by the two eyes competing for the control of cortical territories. In cat and monkey striking structural changes accompany the functional effects of monocular deprivation. Also, in the rat, monocular deprivation causes functional alteration at the level of visual cortex; no structural correlates of these effects, however, have so far been described. Parvalbumin is a calcium binding protein that in the neocortex colocalizes with a subpopulation of GABAergic neurons. Here we report that in the rat monocular deprivation results in a dramatic reduction of parvalbumin-like immunoreactivity in the visual cortex contralateral to the deprived eye. This effect is due to competitive phenomena and not to visual deprivation itself, it is restricted to the binocular portion of the visual cortex and neither binocular deprivation, nor dark rearing can induce it. We conclude that parvalbumin-like immunoreactivity is a useful immunohistochemical marker for the effects of monocular deprivation in the rat visual cortex.

Animals↗
PubMed1992

Nerve growth factor (NGF) prevents the shift in ocular dominance distribution of visual cortical neurons in monocularly deprived rats.

The hypothesis that NGF could play a role in the plasticity of the developing mammalian visual cortex was tested in monocularly deprived (MD) rats. In particular, we have asked whether an exogenous supply of NGF could prevent the changes in ocular dominance distribution induced by monocular deprivation. Hooded rats were monocularly deprived for 1 month, starting at postnatal day 14 (P14), immediately before eye opening, by means of eyelid suture. In eight rats, only monocular deprivation was performed; in eight rats, monocular deprivation was combined with intraventricular injections of beta-NGF, and in three rats, with intraventricular injections of cytochrome C. Injections (2 microliters) were given every other day for a period of 1 month. Single neuron activity was recorded in the primary visual cortex of MD rats, MD rats treated with NGF, and MD rats treated with cytochrome C at the end of the deprivation period, and in normal rats of the same age. We found that monocular deprivation caused a striking change in the ocular dominance distribution of untreated MD rats, reducing binocular cells by a factor of two and increasing by a factor of eight the number of cells dominated by the nondeprived eye. In MD NGF-treated rats, the ocular dominance distribution was indistinguishable from the normal. Cytochrome C treatment was completely ineffective in preventing the ocular dominance shift induced by monocular deprivation. To test whether NGF affected cortical physiology or interfered with transmission of visual information, we evaluated in NGF-treated rats the spontaneous discharge and the orientation selectivity. We found these functional properties to be in the normal range. We conclude that NGF is effective in preventing the effects of monocular deprivation in the rat visual cortex and suggest that NGF is a crucial factor in the competitive processes leading to the stabilization of functional geniculocortical connections during the critical period.

Animals↗
PubMed1991

Different effects of intracranial and intraorbital section of the optic nerve on the functional responses of rat retinal ganglion cells.

A lesion to the optic nerve of adult mammals leads to the retrograde degeneration and finally to the death of injured retinal ganglion cells. In this study, we have evaluated the effects induced by different sites of axotomy on the functional changes occurring in the retinal ganglion cells after optic nerve section. We have investigated the functional properties of retinal ganglion cells of adult rats by recording the retinal responses to patterned stimuli (pattern electroretinogram) after unilateral section of the optic nerve at two different levels: intraorbital and intracranial. The results show that the site of lesion of the optic nerve affects the time of disappearance of the pattern electroretinogram. The pattern electroretinogram takes longer to be degraded after an intracranial section than an intraorbital section.

Animals↗
PubMed1979

A perceptual phenomenon and its neurophysiological correlate.

A square-wave grating from which the fundamental harmonic has been subtracted (missing fundamental grating) when viewed from a suitable distance appears similar to another grating of periodicity three times higher. The neurons of the visual cortex of the cat, in a given range of spatial frequencies characteristic of each cell, give similar responses to the two gratings.

Animals↗
PubMed1979

Responses of visual cortical cells to periodic and non-periodic stimuli.

1. The activity of neurones of the visual cortex (area 17) has been recorded in anaesthetized cats in response to gratings of different profile and to single light and dark bars. 2. At very low spatial frequencies, outside the frequency response range to sinusoidal gratings, the response to square-wave drifting gratings is obtainable from a combination of the response to the single bars of the grating presented in isolation. At higher spatial frequencies this is no longer true. 3. At very low spatial frequencies the responses to square-wave gratings and to missing-fundamental gratings (obtained by subtraction from the square-wave grating of its fundamental gratings (obtained by subtraction from the square-wave grating of its fundamental harmonic) are very similar. 4. At spatial frequencies near the peak of the spatial frequency tuning curve of the cell, the responses to square-wave grating and to sinusoidal gratings are very similar. At these spatial frequencies the response to the missing-fundamental grating is practically zero. 5. At spatial frequencies lower than that of best sensitivity for the cell, the response to square-wave gratings is correlated with the 1st and 3rd harmonic of the stimulus. 6. We conclude that at very low spatial frequencies of the grating the response of cortical cells is correlated with the light or dark edges (or light or dark bars) of the stimulus, because the edges contain high frequencies within the range of sensitivity of the cells. At higher spatial frequencies the results are interpreted best by assuming that cortical cells respond to the harmonics of the visual periodic stimulus. 7. When a background of dynamic visual noise is added to increase the spontaneous discharge of simple cells, their response to visual stimuli becomes linear or quasi-linear. The stimuli could be either single bars or gratings.

Action Potentials↗
PubMed1979

Erythropoietin-dependent primary pure erythrocytosis.

We investigated the pathogenesis of isolated erythrocytosis of 14 yr duration in a 28-yr-old man. The increase in red cell mass was attributed to increased erythropoietin production. An extensive search for recognized causes of secondary erythrocytosis was unrevealing. Family members were found to be hematologically normal. After reduction of the circulating red cell mass by 20%, erythropoietin activity nearly quadrupled, thus suggesting a normal erythropoietin response to phlebotomy. When bone marrow cells of the patient were cultured in plasma clots in the absence of added erythropoietin, endogenous erythroid colony formation was observed, a pattern previously believed to be specific for polycythemia vera bone marrow cells. Our observations suggest that the erythrocytosis in this individual is best explained by an abnormal "servoregulatory" mechanism of erythropoietin production. In addition, this is the first instance in which the rule that endogenous erythroid colony formation is correlated with the diagnosis of polycythemia vera has not held.

Adult↗
PubMed1978

Selective impairment of contrast sensitivity in kittens exposed to periodic gratings.

1. Kittens were exposed to a periodic grating orientated vertically during the critical period of their life. 2. At the end of the critical period the amplitude of the response to drifting gratings was found to be reduced at the spatial frequency of exposure in multi-unit and in some single unit recordings at lateral geniculate level. 3. The contrast sensitivity measured with behavioural methods also showed a depression at the spatial frequency of exposure. 4. An analysis of the preferred stimulus orientation of cortical units in area 17 showed that all orientations were represented.

Action Potentials↗